Here's how to blur the background using the Magnetic Lasso Tool in Photoshop, along with some caveats and alternative suggestions:
Steps Using the Magnetic Lasso Tool:
1. Open your Image in Photoshop: File > Open, and navigate to your image.
2. Select the Magnetic Lasso Tool: Find it in the toolbar (it's grouped with the regular Lasso Tool and Polygonal Lasso Tool). You may need to click and hold the Lasso Tool icon to reveal the others, and then select the Magnetic Lasso Tool.
3. Adjust Settings (Important!): At the top of the screen, in the options bar for the tool, adjust these settings:
* Width: This determines the range within which the tool will "snap" to edges. Start with a lower value (e.g., 5-10 pixels) and increase it if it's not sticking well. Too high and it will attach to the wrong edges.
* Contrast: This affects how sensitive the tool is to differences in color and brightness. A higher contrast setting will make it more likely to stick to edges with strong contrast. A lower setting is better for subtle edges.
* Frequency: This determines how often the tool places anchor points. Higher frequency = more anchor points = more precise (but slower). Lower frequency = fewer anchor points = less precise (but faster). Start with a moderate value (e.g., 50-60) and adjust as needed.
* Tablet Pressure to Size: This option is great if you are using a tablet and allows the width to change based on the pressure that you apply.
4. Create the Selection:
* Click once on the edge of the subject where you want to start your selection.
* Slowly move the mouse along the edge of the subject. The tool will automatically try to snap to the edge.
* Click to manually add anchor points in areas where the tool is struggling to find the edge. This is especially important around hair or intricate details.
* Correct Mistakes: If the tool makes a mistake, press the Delete key to remove the last anchor point. Then, continue tracing.
* Close the Selection: Bring the cursor back to the starting point. A small circle will appear next to the cursor. Click to close the selection.
5. Inverse the Selection: Go to `Select > Inverse`. This selects the *background* instead of the subject. You can also use the keyboard shortcut: `Ctrl+Shift+I` (Windows) or `Cmd+Shift+I` (Mac).
6. Feather the Selection (Crucial!): Go to `Select > Modify > Feather`. A feather radius of 1-3 pixels is usually good for high-resolution images. This softens the edge of the selection, creating a more natural transition between the sharp subject and the blurred background. Without feathering, the blur will have a harsh, unnatural edge. Experiment with the radius until you get the desired result.
7. Apply the Blur:
* Go to `Filter > Blur > Gaussian Blur`.
* Adjust the Radius slider to control the amount of blur. Start with a small value and increase it until you achieve the desired effect. Be careful not to over-blur, as it can look unrealistic.
* Click OK.
8. Refine Edges (Optional): Even with feathering, you might see some halos or unnatural edges. You can use the Clone Stamp Tool (set to a low opacity and a soft brush) to blend the edges further. Alternatively, consider using a mask with a soft brush to refine the selection.
9. Save Your Work: File > Save As, and save your image as a PSD (Photoshop) file to preserve the layers, or as a JPEG for sharing.
Important Considerations and Alternatives:
* Complexity of Edges: The Magnetic Lasso Tool struggles with complex edges, especially hair.
* Contrast: It relies on contrast differences, so it may not work well in areas with subtle color or brightness changes.
* Alternatives:
* Quick Selection Tool + Refine Edge: This is often a much better starting point. Use the Quick Selection Tool to roughly select the subject, then click "Select and Mask" (formerly "Refine Edge") in the options bar. The Select and Mask workspace allows you to precisely refine the selection, especially around hair, using tools like the Edge Detection Brush and the Refine Hair button.
* Select Subject: Photoshop has gotten very good at automatically selecting the subject. `Select > Subject`. Then, refine the selection in the Select and Mask workspace.
* Pen Tool: For maximum precision, use the Pen Tool to manually draw a path around the subject. Convert the path to a selection, and then feather it. This takes more time, but the results are often the best.
* Masking: Instead of directly inverting the selection and blurring, consider using a layer mask. Create a layer with the background blurred (duplicate layer, blur it), and then create a mask based on your selection. This is non-destructive and easier to edit later.
Example Scenario and Tweaks:
Let's say you're blurring the background of a portrait taken outdoors with the subject having fine, flyaway hair:
1. Try Select Subject first: If it does a good job, great! Go to Select and Mask and use Refine Hair.
2. If Select Subject fails: Use the Quick Selection Tool for the bulk of the selection.
3. For the Hair: Switch to the Select and Mask workspace. Use the Edge Detection Brush to paint along the edges of the hair. Adjust the "Shift Edge" slider to contract or expand the selection slightly to eliminate halos.
4. Output: Choose "New Layer with Layer Mask" in the Output Settings of the Select and Mask workspace.
5. Blur the Background Layer: Select the layer *below* the subject layer, and apply the Gaussian Blur.
In summary, while the Magnetic Lasso Tool *can* work, be aware of its limitations. For the best results on portraits, explore the Select Subject, Quick Selection Tool with Refine Edge, and Pen Tool techniques, and always feather your selections!